Specifying New Congestion Control Algorithms. Sally Floyd and Mark Allman draft-floyd-cc-alt-00.txt November 2006 TSVWG Slides: http://www.icir.org/floyd/talks.html. What is the problem?. The problems: There are many proposed congestion control mechanisms.

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“In environments where standard congestion control is able to make reasonable use of the available bandwidth the proposed change should not significantly change this state.”

“For instance, in a situation where each of N flows uses 1/N the network capacity, a new congestion control scheme should not significantly deviate from this state. For instance, a flow using an alternate congestion controller that took half the capacity and left each of the remaining N flows with 1/2N of the capacity would be suspect.”

“An assessment of proposed algorithms in difficult environments such as paths containing wireless links and paths with reverse-path congestion. In addition, proposed algorithms should be evaluated in situations where the bottleneck has high and low levels of statistical multiplexing.”

“A particularly important aspect of evaluating a proposal for standardization is in understanding where the algorithm breaks down. Therefore, particular attention should be paid to extending the investigation into areas where the proposal does not perform well.”

“All alternate congestion control algorithms ultimately should include some notion of "full backoff". That is, at some point the algorithm should reduce the sending rate to one packet per round-trip time and then exponentially backoff the time between single packet transmissions if congestion persists. Exactly when this "full backoff" comes into play will be algorithm-specific. However, this requirement is crucial to protect the network in times of extreme congestion.”

“The proposal should explore how the alternate congestion control mechanism performs with misbehaving senders, receivers, or routers. In addition, the proposal should explore how the alternate congestion control mechanism performs with outside attackers. This can be particularly important for congestion control mechanisms that involve explicit feedback from routers along the path.”

Clarify the fairness section. This is not saying that strict TCP-friendliness should be a requirement.

Clarify that as an alternative to Full Backoff, a flow could stop sending when the allowed sending rate is below a certain threshold.

Clarify that the Full Backoff bullet does not require that different flows with different round-trip times use the same criteria about when they should back off to one packet per round-trip time or less.